The present invention relates to apparatus and methods for determining the date of periodic occasions, such as holidays, and date converters for converting dates back and forth between Gregorian calendars and non-Gregorian calendars.
Calendars are based to a large extent upon the major natural cycles; the rotation of the earth (the 24 hour day), the revolution of the moon around the earth (the lunar month) and the revolution of the earth around the sun (the solar year). The importance of these cycles is that many events in nature are determined by them, and that these events of nature have had implications for both primitive and advanced economies. For example, the growing seasons (spring, summer, fall, winter) are determined by the position of the earth with respect to the sun, whereas the tides are determined primarily with respect to the position of the earth with respect to the moon (and to a lesser extent the position of the earth with respect to the sun). A major aim of all calendars has been to accurately describe these natural cycles and hence make these natural events and their economic consequences more predictable. A major task of all calendars has been to reconcile the different periodicities of these cycles.
For example, a solar year is approximately 365 days, but is not exactly 365 days. The aim of many calendars has been to ensure that the seasons (as represented by a calendar's date for the solstices and equinoxes) remain the "same" every year. To make the calendar more accurate, the Julian calendar (also referred to as the "old civil calendar" and which is the official calendar adopted by Julius Caesar and the Roman Empire) added an extra day in every year divisible by four (i.e., a "leap year", every four years). For even greater accuracy, the Gregorian calendar (also referred to as the "modern civil calendar" and used as the official calendar of most Western nations, including the United States) eliminated leap year in those "century" years which are not divisible by 4 (e.g., there was no leap year in the year 1900 AD because 19 is not divisible by 4).
Consider the example of the lunar month which is approximately 30 days. In fact, it is between 29 and 30 days. But a "year" of 12 lunar months is only a fraction of a day more than 354 days. The Gregorian calendar retains its accuracy with respect to the sun by allowing its 12 months to exceed 30 days and to depart from the lunar cycle. On the other hand, the Islamic calendar is based solely on the lunar month with a "year" consisting of 12 lunar months, and regularly scheduled "leap years" with an extra day. For the Islamic calendar the start of every year will have the same relationship to the lunar cycle, but not the same relationship to the (solar) seasons of the year.
The Hebrew calendar also contains 12 lunar months, but it adds an extra 29 day month seven times every 19 years so that the calendar stays approximately in line with the seasons. The Chinese calendar is also based upon a lunar month and has another (different yet similar) method of reconciling the lunar and solar cycles. Other calendars have different, but well defined, methodologies for achieving these ends.
In addition, many calendar systems divide the passage of time into 7 day weeks, with one particular day having special religious significance as a day of rest (e.g., Friday for Moslems, Saturday for Jews, Sunday for Christians). In some religions, certain religious holidays must occur on particular days of the week.
Not only do different religions have different holidays, but different religions may base their holidays on different calendars. Some religions use different periodicities for different holidays. For example, those Christian holidays termed "immovable feasts" (e.g., Christmas) have been based on a solar cycle such as the Gregorian calendar. Other Christian holidays termed "movable feasts" (e.g., Easter, Lent) are based upon multiple cycles (Easter being essentially the first Sunday after the first new moon after the spring equinox with some other adjustments).
In any event, these natural cycles and subsequent calendars, as well as related religious holiday schedules, are mathematically well defined, although not easily accessible to the lay-person. In addition, to one knowledgeable in the art, the calculations that must be performed to find the date in one calendar system for another event or holiday defined in another calendar system or by other such cycles are straightforward, although sometimes tedious.
Printed calendars and date books are common and frequently show holidays, but are limited not only by the space on the printed page, but also by the calendar system employed. For example, a Gregorian-based calendar or Book-of-Days can easily show that Christmas occurs on December 25 of each Gregorian year, but it can only show Easter (and other Christian moveable feasts or holidays based upon other calendar systems) for one particular year. Each year must be listed separately for these holidays, thereby eliminating much of the calendar's convenience. The issue is not resolved by standard perpetual calendars.
A calendar document can reference more than one calendar system. For example, "The Comprehensive Hebrew Calendar", published by Feldheim Publishers, Nanuet, N.Y., copyright 1986, contains side-by-side renderings of both the Gregorian calendar and the Hebrew calendar (with Jewish holidays noted) for the years 1900 to 2100. However, this "double" calendar requires more than 400 pages to accomplish its task.
Furthermore, there are software programs which address particular holidays. Several software programs give Gregorian dates for Jewish holidays. Some programs address Christian moveable feasts. Greeting card and calendar software include some limited holiday calendaring features.
Various websites on the Internet examine holiday issues. For example, the Indonesian National Holidays posted on http://hastu.com/holidays.html include Gregorian calendar dates for several years for Indonesian Independence Day (based on the solar calendar), 6 Moslem holidays (based on the Hijriyah lunar calendar system), 3 Christian holidays (based on the Metonic cycle and Gregorian calendar), one Hindu holiday (based on the Saka/Caka calendar system) and one Buddhist holiday (based on the Indonesian Buddhist calendar system). Many of these holiday related sites are listed at the CalendarLand website (at http://www juneau.com/home/janice/calendarland/cultural-religious).
Information searching on the Internet is time-consuming. The accuracy of information obtained on the Internet cannot be verified and conflicting information cannot be resolved. The software products and Internet information may have depth, but remains parochial, listing many holidays for many years but only for one religion or ethnicity. Other efforts provide less depth but more breadth, listing several religions but fewer holidays for each one, or for only several years. None of the offerings appear to provide easy and quick access to an encyclopedic approach to the desired information.
Furthermore, the software products and Internet information are generally read-only devices for retrieving information. There is no facility to add information on an as-needed basis for a particular individual's needs.
Many holiday greetings and courtesies to friends or business associates are put off or forgotten because there is no easy or certain way of determining the date of the holiday and the appropriate greeting. In many instances, searching out the information has lower priority than other tasks at hand. In other instances, a person simply doesn't know or think to ask about holidays of other cultures or religions. Individuals may commit serious holiday faux pas through ignorance (for example, inviting a client who is a Moslem to lunch on a Moslem fast day). As commerce becomes more international and more multicultural, easy access to basic ethnic holiday customs becomes essential to building rapport between business contacts.
Accordingly, there is an unmet need for apparatus and methods which allow a user to quickly and easily obtain occasion information associated with Gregorian and non-Gregorian calendars, and to convert dates between such calendars. Furthermore, there is a need to obtain occasion information and to perform calendar conversions when using an intelligent agent to execute tasks. The present invention fulfills such needs.